1. Field of the Invention
This invention relates to globoid worm type rotary machines such as compressors, expanders, evacuators or the like.
2. Description of the Prior Art
Globoid worm type compressors, expanders or evacuators are well known which comprise a globoid worm type rotor housed in a casing and pinions cooperating with the rotor to form compression chamber defined by the casing, the worm rotor and the pinions whereby rotation of the worm rotor causes suction, compression and delivery of gas. There are various types of such pinions.
From the nature of the globoid worm type compressor or expander, sealing for the compression or expansion chamber must be provided between the top of the worm rotor and the casing, between the bottom of the worm rotor and the teeth of the pinion, between the both side surface of the pinion teeth and the side surface of the thread of the worm rotor, and between the aperture portion of the casing and the flat surface of the pinion teeth.
While, because the casing is stationary, it is relatively easy to attain accurate contact between the casing and the top of the worm rotor and between the aperture portion of the casing and the flat surface of the pinion teeth in the process of their machining and assembly, the contact between the grooved surface of the worm rotor and the tip of the tooth of the pinion, both being complicatedly curved for sliding engagement when rotated, is difficult to make so accurate as to attain constant sealing. In addition, the teeth of the pinion is arranged at 90.degree. to the worm rotor, it is difficult to assemble the worm rotor and the pinion so that the entire side surface of the pinion tooth will perfectly contact the entire groove of the worm rotor. As a matter of fact, the mechanical efficiency is scattered over a range of between the maximum and minimum amounts of the efficiency.
To cover such error in accuracy, various means have been used, as shown in French Patent No. 1,331,998 or Japanese Patent Application Forced Publication Sho 48-27303, to improve efficiency, such as making the pinion teeth of plastic material, fastening plastic teeth on the shaft of the pinion by means of spring washers to permit them to shift slightly only in the circumferential direction by the torsional elasticity of the spring washers, fixing the pinion on a support therefor by means of pins with elastic members interposed to permit the pinion tooth to shift only in the circumferential direction, notching the root of the pinion tooth to allow its bending to conform to the surface of contact of the worm rotor.
In these prior art means, however, the center hole of the pinion snugly fits the shaft of the pinion or support therefor only for rotation so as to permit a shift only in the circumferential direction with the shaft of the pinion as the fulcrum. Also in the case using notches, the teeth of the pinion are allowed to bend about the notches to shift in the direction of rotation but not allowed to move in diametric direction at all. Moreover, the rotatative shift about a certain point gives different displacement to points near the fulcrum and points far from it and, therefore, when a point near the fulcrum, that is, the root of the tooth, engages the worm rotor, the tip of the tooth gets farther spaced apart from the worm rotor causing leakage of gas there with a resulting decrease in the machine efficiency while the opposite side of the tooth in the circumferential direction is strongly forced against the worm rotor causing a loss of power.
In the case where the tooth is notched at its root to bend thereat, the same result as mentioned above will come out with the notch at the root as fulcrum and, in addition destructive stress will concentrate there causing a large decrease in durability.
The prior art will now be described with reference to the drawings.
FIG. 1 shows, in transverse cross-section, a conventional globoid worm type compressor, wherein the worm rotor 1 is supported by bearings 3 and 4 and driven by power through a shaft 5. As the worm rotor 1 rotates, pinion teeth 2 meshing therewith rotate about shafts 6. The casing 7, together with the worm rotor 1 and the pinion teeth 2, define a compression chamber 8 in it. Gas is drawn through inlet opening 9, introduced into the compression chamber 8, and then sealed by the teeth of the pinion, compressed as the volume of the compression chamber 8 gradually decreases with the rotation of the worm rotor, and discharged through outlet opening 10.
FIG. 2 shows one disclosed in FIG. 7 of French Patent No. 1,331,998, in which, as shown, the pinion teeth 2 of plastic material are tightly fitted together with a metallic support 11 to the shaft 6 of the pinion and is fastened to the shaft 6 by means of its flange 12 and a nut 14 with a spring washer 13 interposed to give more or less torsional elasticity in the circumferential direction. As seen from the figure, a slight shift in only one circumferential direction is permitted but no displacement of the pinion tooth in the diametric direction is permitted because the pinion 2 is snugly mounted on the shaft 6 for the pinion.
FIG. 3 shows FIG. 5 of Japanese Patent Application Forced Publication Sho 48-27303, in which the pinion 2 is mounted on a support 11 by means of a pin 15 secured thereto with a resilient member 16 interposed. Since the pinion teeth 2 is tightly fitted around the outer periphery 18 of the boss 19 of the support 11, the displacement of the tooth, if allowed owing to the elasticity of the resilient member 16, can take place only in one circumferential direction with the center of the periphery 18 of the boss 19 as fulcrum, but not in the diametric direction.
FIG. 4 shows FIG. 9 of Japanese Patent Application Forced Publication Sho 48-27303, in which each tooth of the pinion teeth 2 is notched at its root as at 20 to narrow the width of the tooth root 22 so that it can readily bend there to adapt itself to the thread of the worm rotor 1. Its displacement, also in this case, is permitted only in one circumferential direction with the notched portion 20 as the fulcrum but no displacement is permitted in the diametric direction. In addition the teeth of the pinion will be damaged soon because of the concentration of destructive stress at the notches 20.
It is apparent that in all of the prior art devices mentioned above, displacement in the diametric direction is impossible though displacement in the circumferential direction may be allowed. Therefore, when the tip 21 of the tooth 2 of the pinion strikes the worm rotor, it cannot be relieved and causes loss of power. What is more undesirable is that the displacement in the circumferential direction takes place with the periphery 18 of boss 19 as the fulcrum or with the notched portion 20 as the fulcrum and therefore, when the root portion (b) of the tooth strongly strikes the worm rotor 1, it is made to shift with the notched portion 20 or the periphery 18 as the fulcrum, so that its tip (a) undergoes more displacement and becomes more spaced from the worm rotor 1 resulting in a leakage there and loss of efficiency while the opposite point (c) more severely strikes and rubs the worm rotor thus causing more loss of power.